1) Field of the Invention
The present invention relates to an ignition device for use in an internal combustion engine in which a spark plug and an ignition coil are integrated with each other, and further to a manufacturing method therefor.
2) Description of the Related Art
So far, as ignition devices for use in internal combustion engines, there have been proposed various types (see Japanese Patent Laid-Open Nos. 2000-252040 and 2000-277232 and European Patent Laid-Open No. 0907019). In such types of ignition devices, a center electrode and a stem are built in a ceramics-made insulator, and each of a primary winding and a secondary winding are wound around a resin-made spool.
Meanwhile, the present inventors have studied the replacement of one of two spools with a ceramic type and the formation of an insulator 5 in which a plug side tube section 51, internally including a center electrode and a stem, and a coil side tube section 52 forming the ceramic spool are integrated with each other as shown in FIG. 5 for the purpose of the cost reduction based on the structural simplification. However, this has indicated the following problems.
That is, in this case, the overall length of the insulator 5 becomes prolonged, which creates problems in that cracks or bends occurs at calcining and the dimension accuracy after calcining deteriorates. Incidentally, although these problems are solvable if a calcined material is internally whittled to form a hollow configuration, this increases the manufacturing cost significantly and, hence, is of no practical use.
In addition, for the plug, the interior of an insulator is packed with a seal material made of a mixture of copper and glass so that the seal material is melted and then solidified to form a seal layer. However, in a case in which the plug side tube section 51 and the coil side tube section 52 are integrally constructed as shown in FIG. 5, since the seal material is put thereinto through an opening of the coil side tube section 52 forming a deep hole, difficulty is experienced in carrying out the packing operation.
Still additionally, in the formation of the seal layer, there is a need to press down the stem through the use of a jig for the purpose of preventing the lift of the stem resulting from the expansion of the seal material and the jig is required to be inserted through the opening of the coil side tube section 52. However, difficulty is encountered in accomplishing the jig insertion work and in maintaining the stem pressed state by the jig.